TIL: Very useful Linux/Unix commands

Here is a list of useful unix commands or code parts. Who does not know it? You have a problem and looking for a solution where you find at stack overflow or similar pages? Here I collect all the commands that I have encountered over time or whose switch I simply can not remember (or want).

  • How do I find all files containing specific text?
    grep -rnw '/path/to/somewhere/' -e 'pattern'
  • How i change the default file permissions (mask that controls file permissions)
  • Untar (unzip) file/folder
    tar -zxvf archive.tar.gz
  • Tar (zip) file/folders
    tar -cvzf archive.tar.gz file1 file2
  • Copy files via rsync from one host to another
    rsync -avz [USER@]HOST:SOURCE rsync://[USER@]HOST[:PORT]/DEST
    rsync -avz -e "ssh -p 12345" LOCAL/SOURCE [USER@]HOST:DEST
  • Using rsync with sudo on the destination machine
    1. Find out the path to rsync: which rsync
    2. Edit the /etc/sudoers file: sudo visudo
    3. Add the line <username> ALL=NOPASSWD:<path to rsync>, where username is the login name of the user that rsync will use to log on. That user must be able to use sudo

Then, on the source machine, specify that sudo rsync shall be used:

rsync -avz --rsync-path="sudo rsync" SOURCE [USER@]HOST:DEST
  • Preserve SSH_AUTH_SOCK (Environment Variables) When Using sudo
    sudo --preserve-env=SSH_AUTH_SOCK -s
  • nslookup missing? Install dig
    sudo apt-get install dnsutils
  • find without "Permission denied"
    find / -name 'filename.ext' 2>&1 | grep -v "Permission denied"
  • flush dns cache
    sudo systemd-resolve --flush-caches
  • show open ports
    netstat -tulpn
  • Directory size
    du -sh /var
    du -shc /var/*
    du -h --max-depth=1 /var
    du -sh /var/lib/docker/containers/*/*.log
  • Search multiple PDF files for a "needle"
    pdfgrep -i needle haystack*.pdf
  • Show hidden files with ls
    ls -lar
  • Redirect STDOUT and STDERR to a file
    nice-command > out.txt 2>&1
  • Installs your SSH public key to a remote host
    sh-copy-id 'user@remotehost'
  • A command-line system information tool
  • Show disk usage, folder size, items per folder, find big directorys, ... with ncdu
  • Fancy resource monitor
  • Display Network usage
    iftop or iptraf
  • Cleanup Docker
    docker system prune --help
  • Find and repair disk errors on ext (ext2, ext3 and ext4) filesystems
    sudo e2fsck -f </dev/sda2> 

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